Question: Divide.
Explanation: Let's turn $3.9$ into tenths using a place value chart. Ones $.$ Tenths $3$ $.$ $9$ $3.9 = 39\text{ tenths}$ Now, lets divide our tenths by the whole number. $39\text{ tenths}\div3 = 13\text{ tenths}$ Last, let's convert $13\text{ tenths}$ into decimal form. Ones $.$ Tenths $1$ $.$ $3$ Here is the completed equation: $1.3=3.9 \div 3$